The invention is in the field of sensor technology and concerns a process and a device for the detection or determination of the position of edges or of edge-like, narrow boundary surfaces of objects, particularly edges of very thin objects, such as paper or transparent foils.
It is known how to detect objects and edges of objects with light barriers (e.g., edge moves relative to the light barrier). Detection of the position of an edge or an object is also known (e.g., light barrier moves relative to the edge). For this, a light-emitting light source and a light-sensitive sensor device, which is positioned in the beam path of the emitted light, are utilized. The sensor device provides a sensor signal, which corresponds to the light intensity impinging on the sensor device. If an object is moved through the light beam between the light source and the sensor device, the intensity measured by the sensor is reduced as soon as a leading boundary surface or edge reaches the light beam. The measured intensity remains at the reduced value until a trailing boundary surface or edge of the object passes the light beam, at which moment the measured light intensity returns to its original value. The two steps in the measured intensity of the received light, for example, are interpreted as the leading and the trailing boundary surface or edge of the object moving through the light beam and are utilized for the measuring or positioning of the object. Reduced and not reduced intensity value can also be interpreted as the presence or absence, respectively, of an object in the field of the light barrier and can be correspondingly utilized.
The process of the known light barrier briefly described above is obviously only applicable for objects that are not transparent to the light beam used as the light barrier. This is, of course, valid not only for visible light, but also for other electromagnetic radiations with a wavelength suitable for a certain application.